The most widely used photographic process is the black-and-white negative–positive system (Figure 1). In the camera the lens projects an image of the scene being photographed onto a film coated with light-sensitive silver salts, such as silver bromide. A shutter built into the lens admits light reflected from the scene for a given time to produce an invisible but developable image in the sensitized layer, thus exposing the film.

During development (in a darkroom) the silver salt crystals that have been struck by the light are converted into metallic silver, ... (100 of 20,799 words)